1. Field of the Invention
The present invention relates to a power detection circuit.
2. Description of the Related Art
An output power detection circuit has recently been used in a wide variety of devices. For example, since a wireless communication terminal, or the like, communicates using an optimal output power at the time of communication with a base station or an access point, an output power detection circuit is essential.
For example, in the following Related Art Document, Patent Document 1 has disclosed a detection circuit having a configuration in which a resistance value is changed according to a level of power input to a detection diode. In addition, the following Patent Document 2 has disclosed a detection circuit having a configuration in which a diode and a resistor are connected in parallel with a capacitor.
However, in the detection circuit, characteristics of a detection voltage for input power exponentially increase as the input power increases. The detection voltage detected in the detection circuit is transmitted to a processing circuit, but a voltage value supplied to the processing circuit is limited. Therefore, it is expected that the detection voltage at a high input power side will exceed the limited value. Also in FIG. 3 of Patent Document 1, since both an input power and a rectifying voltage are represented by a logarithm, in the case in which the rectifying voltage is represented by a real number, the rectifying voltage exponentially increases with respect to the input power. Therefore, it is expected that the detection voltage will become excessively high at the high input power side.
In addition, Patent Document 2 has disclosed a configuration in which a resistance value of a resistor 14 is set to be larger than that of a resistor 19 so that voltage appearing at a detection voltage output terminal 16 at the time of detection is not changed according to a temperature change (please see FIG. 1). However, Patent Document 2 has only disclosed a configuration for compensating for temperature characteristics, but it cannot be expected that characteristics of the detection voltage with respect to the input power are appropriately adjusted.